U.S. patent number 5,112,146 [Application Number 07/731,697] was granted by the patent office on 1992-05-12 for functionally gradated rolling element bearing races.
This patent grant is currently assigned to Rockwell International Corporation. Invention is credited to Maynard L. Stangeland.
United States Patent |
5,112,146 |
Stangeland |
May 12, 1992 |
Functionally gradated rolling element bearing races
Abstract
A bearing assembly including an inner race element and an outer
race element each having raceways therein, the gradated race
matrixes making up the composition of the race elements such that
each race element transitions from a metallic substrate such as
steel to an outer wear resistant layer such as silicon nitride.
Inventors: |
Stangeland; Maynard L.
(Thousand Oaks, CA) |
Assignee: |
Rockwell International
Corporation (Seal Beach, CA)
|
Family
ID: |
24940612 |
Appl.
No.: |
07/731,697 |
Filed: |
July 17, 1991 |
Current U.S.
Class: |
384/492; 384/569;
384/907.1 |
Current CPC
Class: |
F16C
33/62 (20130101); F16C 2206/04 (20130101) |
Current International
Class: |
F16C
33/62 (20060101); F16C 033/62 () |
Field of
Search: |
;384/492,493,513,548,557,569,625,907,907.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Hannon; Thomas R.
Attorney, Agent or Firm: Hamann; H. Fredrick Field; Harry B.
Faulkner; David C.
Claims
What is claimed is:
1. In a bearing assembly including:
(a) an inner race element having a raceway therein;
(b) an outer race element having a raceway therein;
(c) a bearing element carried in said raceway and being movable
relative thereto, the improvement therein being gradated race
elements comprising:
(i) a corrosion resistant metallic sub-matrix layer; and
(ii) an intermediate metallic matrix layer having a hardness
intermediate the metallic sub-matrix and an outer layer of very
hard low friction material the surface of which contacts the
bearing element.
2. The bearing assembly of claim 1 in which the metallic sub-matrix
layer is a high strength corrosion resistant steel.
3. The bearing assembly of claim 1 in which the outer layer
comprises a composition selected from silicon nitride or
diamond-like materials.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to improved race elements in a rolling
element bearing assembly. It is particularly directed to an
improvement in the composition of the race elements accomplished by
functionally gradating the race material composition to optimize
corrosion resistance, thermal expansion, hardness of the raceway,
and minimum friction at the rolling element to raceway
interface.
2. Related Art
Most prior art is for rolling element bearings operating in oil or
a liquid that provides lubrication as well as cooling. For dry
operation or for machinery where the rolling element bearing must
operate in a fluid with low viscuous properties such as cryogenic
propellants, conventional bearing materials cannot be utilized.
Corrosion resistant materials, such as martensitic stainless steel,
are presently used for the races and Teflon (Trademark of E. I.
duPont de Nemours & Co., Inc.) filled fiberglass or silver are
used for the dry lubricating cage or separator.
Recent improvements in rolling element bearings have included
silicon nitride balls or rollers which are much harder and more
wear resistant than martensitic stainless steel. When silicon
nitride balls or rollers are operated with martensitic stainless
steel races, the raceways are the first to wear and spall. In
addition, the martensitic race material thermal coefficient of
expansion is less than that of the typical shaft and housing
materials. The inner race must, therefore, be installed on the
shaft with an interference fit at room temperature in order to
remain piloted at the cryogenic operating temperature. This results
in high hoop stresses in the martensitic stainless steel inner race
which is susceptible to stress corrosion when in the presence of
moisture, resulting in inner race cracking. Conversely, the outer
race must be installed in the housing with a larger than desirable
clearance to compensate for the difference in thermal
contraction.
Various bearing assembly configurations each provided with
lubrication means are disclosed such as for example in the
following documents incorporated by reference.
U.S. Pat. No. 4,362,344 of Dec. 7, 1982, provides a bearing with
stamped, or ground, inner and outer races in which the gap between
the races is filled with a separate rubber sealing ring. In
addition a full complement of bearing elements along with the
desired type and amount of lubricant is assembled between
curvilinear raceways for controlling bearing assembly motion.
U.S. Pat. No. 4,293,171 of Oct. 6, 1981 describes an anti-friction
bearing wherein the rolling elements are coated with an
intermediate metal layer such as by ion plating, said metal layer
having lubricating properties.
However, it is heretofore unknown to provide, in a bearing
assembly, race elements which are functionally gradated to provide
corrosion resistance, desired thermal expansion, hard raceway wear
surface properties, and minimum friction.
SUMMARY AND OBJECTIVES OF INVENTION
Accordingly, it is an object of the invention to provide an
improved bearing assembly.
A further object of the present invention is to provide a bearing
assembly having improved longevity, wear resistance, and a
coefficient of expansion matched to that of the shaft and housing
which contain the rolling element bearing.
Another advantage resides in functionally gradate material of inner
and outer races so:
Bulk of race can be made of a corrosion resistant high strength
steel that is thermally compatible with the shaft and housing
materials and is not susceptible to stress corrosion cracking.
Raceway surfaces can be made of a material that is hard and
resistant to wear and spalling (silicon nitride, ceramics, diamond,
etc.) and potentially has a low coefficient of friction.
Other advantages and objects of the present invention can be found
in the bearing assembly described herein which provides for the
fabrication of bearing inner and outer races where the composition
of the race can be gradated from very hard low friction material at
the rolling element interface to a corrosion resistant base
material that is thermally compatible with the shaft or
housing.
DESCRIPTION OF THE DRAWING
FIG. 1 is a view in vertical sections showing the inner and outer
race elements of a ball bearing assembly according to the
invention.
FIG. 2 is a view of a bearing assembly of the present invention in
which a roller element is juxtapositioned intermediate the inner
and outer race elements.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 and 2 show the most preferred embodiments of the bearing
assembly 10. As depicted, an inner race element 12 having a raceway
14 therein as well as an outer race element 16 having a
complementary raceway 18 compliments shaft 32 and housing 34.
Bearing ball elements 20 carried in said raceways 14, 18 and being
moveable relative thereto is provided in the bearing assembly 10. A
cage or separator 22 maintains equal positioning of bearing balls
20 during rotation. Each race element 12 and 16 is configured to
have a corrosion resistant metallic sub-matrix layer 24 which may
be formed of a high strength corrosion resistant steel. An
intermediate matrix layer 26 which is a mixture of the sublayer and
the outer layer and having a hardness intermediate the metallic
sub-matrix and an outer layer 28 of very hard low friction material
is provided. The outer layer 28, the surface of which contacts
bearing 20, may be made of a very hard low friction material such
as silicon nitride, diamond, or diamond-like materials.
FIG. 2 depicts a bearing assembly in accordance with the present
invention wherein bearing rollers 30 are provided instead of
bearing balls 20. Otherwise the bearing assembly conforms in design
and function to that of the embodiment of FIG. 1.
In operation a bearing assembly according to the present invention
would provide bearings that have low friction, high hertzian stress
capacity, corrosion resistant, and are thermally compatible with
the surrounding components in applications such as in cryogenic
turbopumps, and the like.
* * * * *